The present invention relates to a solid-state image sensor including common elements between the pixels.
The solid-state imaging device using semiconductors are roughly classified in CCDs and image sensors based on CMOS.
The CMOS image sensors generally have the structure which is the so-called 3-Tr APS (Active Pixel Sensor), comprising a photodiode (PD) which converts a photo signal to an electric signal, a reset transistor (RST) which resets the photodiode, a source follower transistor (SF-Tr) which converts signal charges of the photodiode to voltages to output the signal charges in voltage, and a select transistor (Select) which connects/selects pixels and signal lines.
It is said that the solid-state image sensor including 3-Tr-pixels are vulnerable to noises (kTC noises) caused by thermal noises. The structure called a 4-Tr-pixel which can remove kTC noises as well is proposed. The solid-state image sensor including 4-Tr-pixels has the structure including further a transfer transistor (transfer gate) between the rest transistor and the photodiode described above, and an N-type diffused layer (FD: Floating Diffusion) between the reset transistor and the transfer transistor is connected to the gate of the source follower transistor.
The solid-state image sensor including the above-described 4-Tr-pixels requires 4 transistors and 1 photodiode per a pixel unit and has so many component elements. The photodiode has an accordingly decreased occupation area in the pixel. From this viewpoint, it is proposed to make the component elements common between adjacent pixels.
Various layouts for making a read transistor part including the reset transistor, the select transistor and the source follower transistor common between adjacent pixels have been so far reported (refer to, e.g., Japanese published unexamined patent application No. 2000-232216, Japanese published unexamined patent application No. Hei 11-126895 (1999), Japanese published unexamined patent application No. Hei 10-256521 (1998), Japanese published unexamined patent application No. Hei 10-150182 (1998), Japanese published unexamined patent application No. 2001-298177).
Making the read transistor part common between adjacent pixels decreases a element number of 1 pixel, and can increase the occupation area of the photodiode.
However, the proposed pixel layouts having a read transistor part made common between adjacent pixels causes wide variations in photosensitivities and charge transfer characteristics.